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Subject: Re: [PATCH v2 1/3] powerpc/mm: Export flush_all_mm()
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Frederic Barrat <fbarrat@linux.vnet.ibm.com>, Michael Ellerman
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On Wed, 2017-08-30 at 15:59 +0200, Frederic Barrat wrote:
> > It's not clear why it makes sense for these to be empty. Either for the
> > general idea of the "flush_all_mm()" API, or for your intended use by
> > CXL.
> 
> I was not too sure what to do for hash, but the idea is that the new 
> flush_all_mm() is really the equivalent of the old flush_tlb_mm() from 
> before Ben's optimizations for radix, and that was/still is an empty 
> operation on hash, so I kept it that way.
> 
> We don't support hash for capi2 yet. Adding it will definitely require 
> some work in that area, as the current approach (use count on the driver 
> and all TLBIs becoming global when the driver is in use) won't hold much 
> longer.

Why not ? It would work fine on hash, but you do need a way to flush
the TLB when decreasing the count indeed and that's missing for hash.

Cheers,
Ben.